Various catalytic processes involve co-catalysts based on organoaluminum compounds such as TEAL (triethylaluminum), EASC (ethylaluminum sesquichloride), and others. Such co-catalysts may be used in conjunction with other catalysts, e.g., transition metal complexes, to perform various catalytic processes and promote various chemical reactions. Organoaluminum co-catalysts are used in particular for olefin oligomerization processes. For example, organoaluminum co-catalysts can be used in conjunction with transition metal complexes to produce catalyst compositions capable of oligomerizing ethylene (ethene) to 1-butene. Organoaluminum co-catalysts are also used in various olefin polymerization processes. For example, organoaluminum co-catalysts can be used in conjunction with transition metal complexes to produce catalyst compositions capable of generating polyethylene, polypropylene, and other polymers.
1-Butene has for a long time been a desirable substance in the chemical industry. Not only can 1-butene be converted to polybutene-1 and butylene oxides, it can also be used as a co-monomer with ethylene for the production of high strength and high stress crack resistant polyethylene resins. The major industrial routes for producing 1-butene include steam cracking of C4 hydrocarbon streams, ethylene oligomerization processes, refinery operations of crude oil, and ethylene dimerization processes. Catalytic dimerization of ethylene into 1-butene produces higher chain polymers via the growth reaction of the organoaluminum compounds (Ziegler, Angew. Chem. (1952); 64:323-329; J. Boor, Editor, Ziegler-Natta Catalysts and Polymerizations, Acad. Press (New York) 1979; Handbook of Transition Metal Polymerization Catalysts, R. Hoff, R. T. Mathers, Eds. 2010 John Wiley & Sons).
One route to the preparation of 1-butene is the cracking of higher petrochemical fractions containing more than four carbon atoms. A further route to the preparation of 1-butene is via the catalytic dimerization of ethylene. The industrial synthesis of 1-butene can be achieved using nickel or titanium catalysts in large industrial processes such as Alphabutol™ (Handbook of Petroleum Processing, Edited by D. S. J. Jones, P. R. Pujadó; Springer Science 2008; Forestière et al., Oil & Gas Science and Technology-Rev. IFP (2009); 64(6):649-667).
In the Alphabutol™ system and other existing processes for preparation of 1-butene by catalytic dimerization of ethylene, catalyst compositions are formed by combining organoaluminum co-catalysts with transition metal complexes. For example, a solution of an organoaluminum co-catalyst in a hydrocarbon solvent can be mixed with a solution of a titanium complex in an ether solvent to obtain a catalyst composition, which is used to prepare 1-butene, as in the Alphabutol™ system. Such catalyst systems can suffer from drawbacks, which include low catalyst activity, a lengthy induction period, and process fouling, including precipitation of polyethylene. The catalytic activity of the Alphabutol™ system can be relatively low at roughly 1 kg of product per gram of titanium. Polymer formation and lengthy initial induction period are major drawbacks for the commercial Alphabutol™ system.
There remains a need in the art for an organoaluminum co-catalyst composition that is suitable for various processes, including dimerization of ethylene, and is characterized by one or more of improved catalytic activity, shortened induction period, long lifetimes, and high selectivity.